Secret key rate of a continuous-variable quantum-key-distribution scheme when the detection process is inaccessible to eavesdroppers

TL;DR

This paper introduces a method to calculate the secret key rate of a continuous-variable quantum key distribution scheme, accounting for inaccessible detection processes, and demonstrates improved key rates especially with reverse reconciliation.

Contribution

The authors develop a numerical method to evaluate secret key rates considering Gaussian channels with inaccessible detection, enhancing security analysis in CV-QKD.

Findings

Key rates are higher when detection noise is considered inaccessible to eavesdroppers.

The method applies to general Gaussian attacks and is particularly effective with reverse reconciliation.

Asymptotic key rate calculations show significant improvements over traditional models.

Abstract

We have developed a method to calculate a secret key rate of a continuous-variable quantum-key-distribution scheme using four coherent states and postselection for a general model of Gaussian attacks. We assume that the transmission line and detection process are described by a pair of Gaussian channels. In our analysis, while the loss and noise on the transmission line are induced by an eavesdropper, Eve, who can replace the transmission line with a lossless and noiseless optical fiber, she is assumed inaccessible to the detection process. By separating the transmission noise and detection noise, we can always extract a larger key compared with the case that all loss and noises are induced by an eavesdropper's interference. An asymptotic key rate against collective Gaussian attacks can be determined numerically for the given channels' parameters. The improvement of the key rates turns out to be more significant for the reverse-reconciliation scheme.